This project focuses on the development of contraceptive agents to block two steps in fertilization. These agents will be orally available drugs that block either sperm binding to the egg's zona pellucida or sperm entry into the oviduct. To develop the first contraceptive drug, we will identify the sperm surface protein that enables sperm to bind to the egg's zona pellucida. Despite intensive investigation for the last 20 years, the sperm protein with this function remains unknown. In our recent research, we have developed two new mutant mouse lines in which the males are infertile and make sperm that fail to bind to the zona. The availability of these knockout mice, along with new genomic and proteomic technologies, provides us a completely novel approach to this problem. Having identified the sperm's zona binding protein, we will establish a high-throughput assay to screen inhibitors that block binding of the human zona binding protein to human ZP3. This high-throughput screen will be the key that allows subsequent contraceptive development with an industrial partner. For the second contraceptive agent, the starting point will be one of our mouse lines that carries a deletion of the sperm adhesion protein fertilin a. Male mice lacking fertilin a produce sperm that fail to enter the oviduct. We will test the hypothesis that sperm adhesion to the uterine or uterotubal junction epithelium requires fertilin a and that this binding step results in a signal that makes sperm competent to enter the oviduct. We propose assays for fertilin a adhesion to the epithelium and for screening small molecule inhibitors of the adhesion that will cause sperm arrest in the uterus.